You may appreciate the fact that we breathe to get air into and out of our lungs. Have you ever wondered what happens inside the lungs? As we look closely, we can see that gas exchange occurs in the lungs between the air and our blood. Now, gas exchange in the lungs refers to the movement of oxygen into the blood and carbon dioxide out of the blood. Oxygen and carbon dioxide move across what we call therespiratory surface, and that consists of an alveolar epithelial cell and a pulmonary capillary endothelial cell. Now, this respiratory surface is also referred to as the respiratory membrane. Note that the air is on one side of the membrane and blood is on the other side of the membrane. As you can see from the image on the screen, oxygen moves out of the alveolar air into the blood, while carbon dioxide moves in the opposite direction. Therefore, we use the term gas exchange, as oxygen is exchanged for carbon dioxide across the respiratory surface.Gas Exchange Is EfficientOur bodies require a lot of oxygen to help our cells make the energy they need to do work. Likewise, we need to get rid of the carbon dioxide that's made by our cells when they work. Therefore, gas exchange needs to be efficient to get enough oxygen into our body - and ultimately to our cells - and to get the carbon dioxide out of the body. So let's discuss some of the factors that help gas exchange.